PPAPI: Make blocking completion callbacks work.

ppapi/shared_impl/proxy_lock.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ppapi/shared_impl/proxy_lock.h"
 
 #include "base/synchronization/lock.h"
 #include "ppapi/shared_impl/ppapi_globals.h"
 
 namespace ppapi {
 
 // static
 void ProxyLock::Acquire() {
   base::Lock* lock(PpapiGlobals::Get()->GetProxyLock());
   if (lock)
     lock->Acquire();
 }
 
 // static
 void ProxyLock::Release() {
   base::Lock* lock(PpapiGlobals::Get()->GetProxyLock());
   if (lock)
     lock->Release();
 }
 
+void CallWhileUnlocked(const base::Closure& closure) {
+  ProxyAutoUnlock lock;
+  closure.Run();
+}
+
 void CallWhileLocked(const base::Closure& closure) {
   ProxyAutoLock lock;
   closure.Run();
 }
 
 }  // namespace ppapi